Computer tomography (also known as computed tomography or CT) is a technology used to produce images of the interior of an object by irradiating the object, measuring the radiation scatter, and reconstructing images from this measured data to produce an interpretable set of images. CT is frequently employed in medicine to produce images of the inside of a human body to permit evaluation of a patient's medical condition. For instance, radiologists may detect anomalies such as tumors and aneurysms in CT images.
CT images show variations in density of the matter inside an object such as a human body utilizing grayscale images. For instance, a typical conventional CT image uses 12-bit grayscale, but other image encoding standards may be used in other embodiments. The shade of gray in which a particular area of a CT image is displayed corresponds to the radiodensity of that area in the imaged body, as measured in Hounsfield units (HU), where radiodensity is the relative transparency of a substance to x-rays. An area of a lung, for example, being mostly air, is rendered in a relatively dark shade of gray corresponding to an HU value approximating the HU value of air at standard temperature and pressure (i.e., −400 to −1024 HU). An area of an organ, in another example, being mostly of the same radiodensity as water, may be rendered in a relatively light shade of gray corresponding to an HU value that is close to the HU value of water at standard temperature and pressure (i.e., 0 HU). Similarly, muscle, which is denser than water, may be imaged in a lighter shade of gray corresponding to about +40 HU, and cortical bone, which is much denser than water, may be imaged at in an even lighter shade of gray corresponding to about +400 HU.
To be of use in evaluating the medical condition of a patient, a CT image must be interpreted by an expert in the field, generally a radiologist. The expert must bring to bear wide-ranging knowledge of the human anatomy and of the subtleties of CT imaging technology. Despite the advanced nature of the imaging technology and the computer technology used to produce CT images, the radiologist must typically devote significant and valuable time to the analysis and interpretation of an image to produce a correct evaluation of the imaged patient's condition. Radiologists are called upon to interpret an increasing number of images as the use of CT imaging increases.